1. Field of the Invention
The present invention relates to a heat pipe type cooling apparatus for semiconductors.
2. Description of the Related Art
As disclosed in Japanese Patent Disclosure (Kokai) No. 60-57956 by the present inventors, a cooling apparatus for cooling power semiconductors such as a thyristor by using a heat pipe is already known. As shown in Figs. 1A and lB, in this heat pipe type cooling apparatus for semiconductors, fins 2, each of which is made of a metal, such as aluminum or copper, having a high thermal conductivity, extend from heat pipes 1, each of which is made of a metal, such as copper, having a high thermal conductivity so as to constitute a heat dissipation portion. The lower ends of the heat pipes are inserted in metal block 3 made of a metal, such as copper or aluminum, having a high thermal conductivity. With this arrangement, loss heat from semiconductor 4 such as a thyristor attached to the metal block is transferred to the heat pipes, and is cooled down naturally or forcibly by a fan through the fines, thereby increasing efficiency of the semiconductor. Terminal 5 for extracting a current is attached to the block as needed. Since a surface of a semiconductor such as a thyristor generally has a potential, a current flows to the heat dissipation portion through the metal heat pipes. Therefore, handling of the heat pipe type cooling apparatus is dangerous depending on operating conditions. Especially, since such an apparatus is often mounted in a vehicle such as a train and used as a cooling apparatus for an inverter thyristor, a problem of electrical safety is inevitably posed. For this reason, an insulating plate made of a ceramic material, such as aluminum nitride, having a relatively high thermal conductivity is arranged between the semiconductor such as a thyristor and the metal block so as to perform electrical insulation. However, the above aluminum nitride insulating plate poses problems in terms of thermal performance, withstand voltage function, mechanical strength, reliability, and the like.